Fluid-cooled transformer having a temperature responsive indicating and controlling device

ABSTRACT

Temperature responsive device suitable for use with air-cooled power transformers. The temperature responsive device indicates the temperature at a predetermined location within the transformer and controls the activation of fans, alarms, and circuit breakers associated with the transformer. Electrical isolation between a temperature sensing element and the controlled auxiliary apparatus is provided by light channels across which the control information is transmitted.

United States Patent 1191 McElroy 1111 3,849,705 1 1 Nov. 19, 1974 [54]FLUID-COOLED TRANSFORMER HAVING 3,076,897 2/1963 Skirvin 340/228 s ATEMPERATURE RESPONSIVE 3,079,524 2/1963 Gibson et a1 .1 3,131,322 4/1964Pleiss, Jr. et a1. INDICATING AND CONTROLLING DEVICE 3,619,629 11/1971Matthews [75] Inventor: David W. McElroy, Mercer, Pa. 3,688,295 8/1972Tsoras et al 340/228 R 3,808,502 4/1974 Babilius 317/9 R [73] Ass1gnee:Westinghouse Electrlc Corporation, 3309960 5/1974 J i I I 7H3 BPlttsburgh, Pa. 3,312,401 5 1974 Radin 317/1335 2 i 2] Filed July 1973Primary Examiner-J. D. Miller [2 PP 378,285 Assistant Examiner-PatrickR. Salce Attorney, Agent, or Firm-.l. R. Hanway 52 US. Cl. ..31714R 3714 F 3 1 l i /i4 1571 ABSTRACT 51 Int. Cl. H02h 7/04 Temperatureresponsive deviee Suitable for use with 5 Fi l f Search 317/14 R, 14 F14 H, 14 J, air-cooled power transformers. The temperature re- 317/15,41, 40; 340/228 R, 228 S, 243 A, sponsive device indicates thetemperature at a prede- 380; 200/DIG. 36; 250/221; 310/68 C; terminedlocation within the transformer and controls 73 350 359 341; 323 44 Rthe activation of fans, alarms, and circuit breakers associated with thetransformer. Electrical isolation be- 5 References Cited tween atemperature sensing element and the con UNITED STATES PATENTS trolledauxiliary apparatus is provided by light channels across which thecontrol information is transmitl,736,993 11/1929 Brelsky 340/228 S ted2,525,499 10/1950 Peterson et a1..... 317/14 F 2,896,152 7/1959 Schwab3l7/14.5 4 Claims, 3 Drawing Figures TEMPERATURE INDICATOR OFF 180C I 4036 TEMPERATURE 1 FAN COMPENSATOR COMPARATOR A IR c 44x TR 230 5a BREAKERCOMPARATOR BREAKER PATENTmv 1 19M 3, 849,705 sum 10! 2 AMP TEMPERATURE IINDICATOR T OFFI80C 40 l I 36 v TEMPERATURE FAN 54 coMPENsAToRCOMPARATOR FAN so wfiffiim 52 ALARM 44 TRIP 230 c BREAKER K58 COMPARATORBREAKER PAIENIEL IIJV 1 9 I974 mok mwzwo PIG] mOk mw2mo FIG:

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FLUID-COOLED TRANSFORMER HAVING A TEMPERATURE RESPONSIVE INDICATING ANDCONTROLLING DEVICE BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates, in general, to electrical apparatus and, morespecifically to transformers having temperature responsive indicatingand controlling means.

2. Description of the Prior Art Fluid-cooled electrical apparatus, suchas air-cooled transformers, frequently have a fluid forcing device, suchas a pump or fan, to enhance the flow of the cooling fluid around theheat producing components of the apparatus. It is advantages insomeair-cooled transformer applications to monitor a temperature within thetransformer, to indicate the monitored temperature, and to controlauxiliary apparatus, such as fans, in a predetermined manner dependentupon the monitored temperature. Generally, when the monitoredtemperature increases to a predetermined value, one or more fans areturned on in an effort to lower the temperature.

Air-cooled transformers have certain regions, called hot spots, whichexhibit a higher temperature than the surrounding regions due to theinherent upward flow of heated air and to the shape of the heatedstructure. It is the temperature at the hot spot region which determinesthe upper temperature limit within which the transformer may be safelyoperated.

Many prior art temperature monitors use capillary tubes placed near thehot spot-to measure the temperature. Since the hot spot is usuallylocated within a winding of the transformer, normally in the centerwinding of threephase transformers at a location which is aboutone-third of the winding length from the top of the center winding, itis not practical to place the capillary tube exactly at the hot spot.Consequently, the determination of the hot spot temperature must beaccomplished by using empirical data which correlates the temperature atthe hot spot to that at the position where the capillary tube islocated. Thus, some inaccuracies may exist between the indicated hotspot temperature and the true hot spot temperature with the use of theprior art capillary tube arrangements. Therefore, it is desirable, andit is an object of this invention, to provide a transformer having a hotspot indicator with a sensor which may be placed directly into the hotspot region of the transformer.

Indicating the temperature of the hot spot is sufficient in someapplications. However, in other applications, simply indicating thetemperature is not sufficient to protect the apparatus. Therefore, it isalso desirable, an it is a further object of this invention, to providea hot spot indicator which directly monitors the temperature at the hotspot and which controls various alarms and regulating apparatus.

SUMMARY OF THE INVENTION There is disclosed herein a new and useful hotspot indicator and controller for use with electrical apparatus. Theindicator includes a temperature responsive electrical sensing elementwhich is positioned at the hot spot in the apparatus. The electricalsensing element is connected to an amplifier which processes thetemperature responsive signal from the electrical sensing element andapplies the processed signal to an indicator and to comparator circuits.The indicator displays the temperature, in degrees, of the hot spot. Onecomparator governs the temperature at which a cooling fan is turned onand off. Another comparator governs the temperature at which an alarmindicator is turned on. Still another comparator governs the temperatureat which a circuit breaker is tripped. The comparators and the heatsensing element are isolated from the controlled auxiliary apparatus topermit the placement of the heat sensing element at or near a highpotential in the electrical apparatus without the need for largeinsulation structures near the hot spot. Isolation from the auxiliaryapparatus is provided by light channels across which the controlinformation is transmitted. Isolation from the power source is providedby an isolation transformer. The indicator disclosed herein providesaccurate indications of the hot spot temperature and provides programmedcontrol over the operation of auxiliary apparatus, such as fans, alarms,and circuit breakers.

BRIEF DESCRIPTION OF THE DRAWING Further advantages and uses ofthisinvention will become more apparent when considered in view of thefollowing detailed description and drawing, in which:

FIG. 1 is an elevational view of an air-cooled transformer with aportion of the housing broken away;

FIG. 2 is a schematic block diagram of a temperature responsiveindicating and controlling device constructed according to thisinvention; and

FIG. 3 is a diagram of the device shown in FIG. 2 illustrating thepotential isolating circuitry.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the followingdescription, similar reference characters refer to similar elements ormembers in all the figures of the drawing. 1

Referring now to the drawing, and to FIG. 1 in particular, there isshown an air-cooled transformer 10 which is equipped with a temperatureresponsive indicating and controlling device 12. The transformer 10includes a ventilated housing 14, a three-phase magnetic core 16, andphase winding structures 18-, 20 and 22. Forcing means, such as the fans24, enchance the circulation of air around and through the core andwinding as sembly of the transformer 10.

Many prior art temperature responsive devices associated with similartransformers use capillary or bimetallic elements which are not easilyplaced into the hot spot of the transformer. Such elements usually areplaced against a winding lead, such as the bus conductor 26. Thetemperature responsive device of this invention comprises a temperatureresponsive electrical sensing element, such as a thermocouple, or atemperature dependent variable resistance element, such as a thermistor.Because of its size and connecting requirements, the temperatureresponsive element of this invention may be placed directly into thecore and winding structure at the location of the hot spot Although thelocation of the hot spot in various transformers may be different, thehot spot in the transformer 10 shown in FIG. I is located within thephase winding 20 about one-third of the winding length from the top ofthe winding 20. The temperature responsive element which is positionedwithin the winding structure is connected to the control panel 28 by theelectrical cable 30. Circuitry located at the control panel 28 properlysenses the electrical signals from the temperature responsive elementand provides the desired indicating and/or controlling functions. I

FIG. 2 is a schematic block diagram of the temperature responsiveindicating and controlling device 12 connected to appropriate indicatingand controlling components. The thermocouple 32, which is positioned tomeasure the temperature at the hot spot of the transformer, develops avoltage which is transmitted to the amplifier 34 through the cable 30.The temperature compensator 36 reduces the effect of the ambienttemperature on the response of the amplifier 34. Combined amplifiers andtemperature compensators are available commercially in a singleintergrated circuit package for compensated amplification of athermocouple generated voltage.

The amplified signal from the amplifier 34 is applied to a temperatureindicator 38 and to comparators 40, 42 and 44. The temperature indicator38 may be a suitable current or voltage meter having a scale calibratedin temperature degrees. The comparators 40, 42 and 44 compare the signalfrom the amplifier 34 with internal reference signals and activate theirassociated indicators or controls depending upon the adjustment of thecomparator circuit parameters.

The blocks 46, 48, 50 and 52 indicate the presence of adjustable circuitparameters for the comparators. For the fan comparator 40, the circuitmay be adjusted to cause a signal from the comparator 40 to turn the fan54 on when the temperature measured by the thermocouple 32 reaches 205Cand to turn the fan 54 off when the temperature decreases to 180C. Forthe alarm comparator 42, the circuit may be adjusted to cause a signalfrom the comparator 42 to turn the alarm 56 on when the temperaturereaches 220C. For the breaker comparator 44, the circuit may be adjustedto cause a signal from the comparator 44 to trip the circuit breaker 58when the temperature reaches 230C. It is within the comtemplation ofthis invention that any of the comparators may have on-off control withthe proper circuit changes.

The temperatures of operation may be changed without departing from thescope of the invention. Any number of fans may be controlled by the fancomparator 40, or muliple comparators may be used to turn on differentfans at different temperatures. The alarm 56 may be any locally mounteddevice on the transformer, such as a buzzer or light, or a remotelylocated device. Similarly, the circuit breaker 58 may be containedwithin the transformer housing 14 or in the housing of associatedelectrical equipment.

A definite sequence of events may occur with the circuit parametersadjusted to operate the comparators at the temperatures indicated inFIG. 2. The temperature of the hot spot is indicated continuously by thetemperature indicator 38. If the temperature increases to 205C. the fan54 is turned on to help cool the transformer 10. If the fan lowers thetemperature of the transformer to 180C, the fan 54 is turned off. If thetemperature increases after the fan is turned on, the fan continues torun. lfthe temperature increases to 220C, the alarm 56 is activated towarn personnel that the transformer is operating in an overheatedcondition. If the temperature increases to 230C, the circuit breaker 58is tripped to de-energize the transformer 10 or to rcmove the loadfromthe transformer 10, thereby reducing the possibility of damaging thetransformer due to overheating.

The thermocouple 32, and some of the circuitry associated therewith, issusceptible to the high potentials appearing on the winding 20, since itis usually undesirable to provide enough insulation around thethermocouple 32 to fully insulate the high voltages to ground. Thus, aform of electrical isolation between the thermocouple 32 and theauxiliary indicating and controlling elements is desirable.

FIG. 3 illustrates circuitry which provides electrical isolation in thetemperature responsive device 12. The line 60 schematically indicatesthe electrical isolation barrier between the circuit components. Asource of power is connected to a suitably insulated isolationtransformer 62 through the circuit breaker 64. The potential on thesecondary winding 66 of the transformer 62 is isolated from the primarywinding 68 and from the power source.

A suitable power supply 70 rectifies and filters the AC voltage andprovides power to the amplifier 34 and to the comparators 72, 74 and 76.The input voltages are applied across the resistors 78, and 82 to thecomparators 72, 74 and 76, respectively. Variable resistors 84, 86 and88 permit adjustment of the voltage level required to activate thecomparators 72, 74 and 76, respectively. The variable resistor 90permits adjustment of the voltage level required to deactivate thecomparator 72 and turn the fan 54 off.

The output signals from the comparators 72, 74 and 76 are applied to thelight generators 92, 94 and 96 which emit light energy when the outputsignals have a sufficient magnitude. Suitable light generators includelight emitting diodes and incandescent lamps. The light energy emittedby the light generators 92, 94 and 96 is directed to the light detectors98, 100 and 102, respectively, by suitable means, such as by a lensarrangement or through optical fibers.

The light detectors 98, 100 and 102 may be constructed of any suitableelements, such as photocells, light sensitive diodes, or light sensitivetransistors. The path traversed by the light energy must be sufficientlylong enough to provide the desired electrical insulation between thelight generator and the light detector. The

light detectors 98, 100 and 102 are connected to relays.

104, 106 and 108, respectively, which activate the fan 54, the alarm 56,and the circuit breaker 58.

With the circuit illustrated in FIG. 3, high-voltage isolation betweenthe thermocouple 32 and the auxiliary indicators and controls isachieved. Thus the thermocouple 32 may be located within a winding atthe hot spot position. Different hot spot temperatures cause differentindicating and controlling conditions to be activated. Other isolatingarrangements may be used, such as by the use of properly insulatedrelays.

Since numerous changes may be made in the above described apparatus, andsince different embodiments of the invention may be made withoutdeparting from the spirit thereof, it is intended that all of the mattercontained in the foregoing description, orshown in the accompanyingdrawing shall be interpreted as illustrative rather than limiting.

I claim as my invention:

1. A fluid-cooled transformer comprising the combination of:

a core and coil assembly;

temperature responsive means located within thetransformer coil;

means for forcing the cooling fluid around said core and coil assembly,said forcing means being con- 5 trolled by said temperature responsivemeans;

a first comparator circuit which is responsive to the temperature ofsaid temperature responsive means, said first comparator circuit beingconstructed to activate the forcing means at a first predeterminedtemperature and to deactivate the forcing means at a secondpredetermined temperature of said temperature responsive means;

means for providing an alarm if the temperature in the coil becomesexcessively high, said indicating means being activated by saidtemperature responsive means;

a second comparator circuit which is responsive to the temperature ofsaid temperature responsive means, said second comparator circuit beingconstructed to activate the alarm means at a third predeterminedtemperature of said temperature responsive means;

means for interrupting the load power delivered by the transformer, saidinterrupting means being activated by said temperature responsive means;and,

a third comparator circuit which is responsive to the temperature ofsaid temperature responsive means, said third comparator circuit beingconstructed to activate the reducing means at a fourth predeterminedtemperature of said temperature responsive means;

said temperature responsive means being isolated from the forcing,alarm, and interrupting means to prevent the transfer of any highvoltages existing on the temperature responsive means to the forcing,alarm or interrupting means.

2. The fluid-cooled transformer of claim 1 wherein the firstpredetermined temperature is higher than the second predeterminedtemperature, the third predetermined temperature is higher than thefirst predetermined temperature, and the fourth predeterminedtemperature is higher than the third predetermined temperature.

3. The fluid-cooled transformer of claim 1 wherein the forcing, alarm,and interrupting means each include a light generator and a lightdetector which is responsive to said light generator, with the isolationbeing provided by the light channel between said light generator andsaid light detector.

4. The fluid cooled transformer of claim 3 including an isolationtransformer which isolates the power supplied to the first, second andthird comparator circuits from the power source.

1. A fluid-cooled transformer comprising the combination of: a core andcoil assembly; temperature responsive means located within thetransformer coil; means for forcing the cooling fluid around said coreand coil assembly, said forcing means being controlled by saidtemperature responsive means; a first comparator circuit which isresponsive to the temperature of said temperature responsive means, saidfirst comparator circuit being constructed to activate the forcing meansat a first predetermined temperature and to deactivate the forcing meansat a second predetermined temperature of said temperature responsivemeans; means for providing an alarm if the temperature in the coilbecomes excessively high, said indicating means being activated by saidtemperature responsive means; a second comparator circuit which isresponsive to the temperature of said temperature responsive means, saidsecond comparator circuit being constructed to activate the alarm meansat a third predetermined temperature of said temperature responsivemeans; means for interrupting the load power delivered by thetransformer, said interrupting means being activated by said temperatureresponsive means; and, a third comparator circuit which is responsive tothe temperature of said temperature responsive means, said thirdcomparator circuit being constructed to activate the reducing means at afourth predetermined temperature of said temperature responsive means;said temperature responsive means being isolated from the forcing,alarm, and interrupting means to prevent the transfer of any highvoltages existing on the temperature responsive means to the forcing,alarm or interrupting means.
 2. The fluid-cooled transformer of claim 1wherein the first predetermined temperature is higher than the secondpredetermined temperature, the third predetermined temperature is higherthan the first predetermined temperature, and the fourth predeterminedtemperature is higher than the third predetermined temperature.
 3. Thefluid-cooled transformer of claim 1 wherein the forcing, alarm, andinterrupting means each include a light generator and a light detectorwhich is responsive to said light generator, with the isolation beingprovided by the light channel between said light generator and saidlight detector.
 4. The fluid cooled transformer of claim 3 including anisolation transformer which isolates the power supplied to the first,second and third comparator circuits from the power source.